Electrolytic amalgamator

ABSTRACT

ELECTROLYTIC AMALGAMATION INCLUDING POSITIVELY DRIVEN MULTIPLE PULP TREATMENT CELLS COOPERATING WITH A PLURALITY OF SEPARATE MERCURY BED CATHODES WITH THE MERCURY BEING CONSTANTLY RECIRCULATED AND REACTIVATED.

June 29, 1971 R E, MCCHESNEY 3,589,995

ELECTROLYTIC AMALGAMATOR y Filed April 17. 1968 s sheets-sheet 1 FIG,

Auff:

INVENTOR ROBERT EDWARD McCH ESNEY 5%@ @Mgg/W ATTORNEYS.'

June 294, 1971 R, E', MocHEsNEY 3,589,995

' ELEcTRoLYTIc AMALGAMATOR Filed April 17, 1968 s sheets-sheet n "'11 I lr;

llllllllIlI mi l l j 42 68 INVENTOR I4 vRoer-:RT EDWARD MCCHESNEY ATTORNEYf FIG. 3

June 29,1971 R, E, MCCHESNEY ELECTROLYTIC AMALGAMATOR Filed April 17. 1968 3 Sheets-Sheet 3 D EN E T mw M m 6 mmFm n ULOOL/\ *AIHO S H m SS C W O Dn Y E a wm 2 v 6 .N C R I O MTl I.'

MERCURY FROM FILTER FIG. 4

INVBNTOR ROBERT EDWARD MCCHESNEY BWL/m ATTORNEYS.

United States Patent O 3,589,995 ELECTROLYTIC AMALGAMATOR Robert Edward McChesney, Reno, Nev., assignor to McChesney Corporation, Reno, Nev. Filed Apr. 17, 1968, Ser. No. 722,023 Int. Cl. C22d 1/04, 1/02 U.S. Cl. 204-202 2 Claims ABSTRACT OF THE DISCLOSURE Electrolytic amalgamation including positively driven multiple pulp treatment cells cooperating with a plurality of separate mercury bed cathodes with the mercury being constantly recirculated and reactivated.

BACKGROUND OF THE INVENTION The recovery of precious metals from their ores by amalgamation with mercury has been practiced for many years and one of the most effective methods for improving the eiiiciency of such amalgamators involves the use of an amalgam of sodium as the collector. This is preferably formed by electrolyzing a sodium chloride solution with mercury acting as the cathode. Such amalgams are effective when freshly made but deteriorate rapidly since the sodium decomposes the water of the pulp to form sodium hydroxide. The electrolysis of the pulp has many desirable effects but unfortunately in the past it has not been possible to properly control the electrolysis. Further conventional apparatus normally employs water under pressure to move the ore slurry relative to the amalgamated plate or bed of mercury or depends on gravity for movement of the same, placing serious limitations on both control and process speed.

In an attempt to increase the eiciency of mercury sodium amalgam apparatus mercury traps or other spaced projections along the gravity path of conventional apparatus have been employed since, due to the specific gravity of mercury it should seek the lowest level and any lighter material is therefore easily washed across the mercury surface. Unfortunately, in treating ores with heavy black sand fraction (concentrate), the fractions tend to `build up behind any small obstruction until it covers the mercury in a trap or well. The new supply of mercury which enters the apparatus then rolls across the surface of the lighter material and is lost in the tails. This is especially true if the mercury is in the least bit contaminated.

In addition, the use of sodium as the collector in the mercury sodium amalgam, requires the activation of the mercury by treating the same in a sodium generator. But in a matter of seconds after activated mercury is exposed to air or water, it begins a rapid deterioration. This is further complicated when working with complex ores that contain many of the interfering elements and unless the mercury is constantly being activated, it takes on a surface coating and begins a division into smaller and smaller globules. The quick is now floured. This is the plague of all amalgamation and the finely divided quick will come to the surface of the water and float like a cord. Even a large amount of shaking will not rectify this condition and in fact accentuates it.

It is therefore, a primary object of this invention to provide an improved mercury-sodium amalgamator for the recovery of precious metals which close control of electrolysis within the amalgamator is readily achieved by employing a plurality of individual cells in which the pulp is positively moved across a bed of recirculated and reactivated mercury amalgam.

It is a further object of this invention to provide an improved mercury-sodium amalgamator for the recovery ICC of precious metals which allows close control of the rate of' ore pulp feed, the electrolyte in contact with the pulp, the dilution of the electrolyte caused by the feed of the pulp, the rotation time of the ore slurry in contact with the mercury-sodium amalgam and the electrolysis parameters of the apparatus.

Other objects of the invention will be pointed out in the following detailed description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode which'has been contemplated of applying the principle.

-In the drawings:

FIG. 1 is an elevational view of the improved mercurysodium amalgamator of the present invention.

FIG. 2 is an elevational view of a portion of the apparatus shown in FIG. l taken about lines 2 2.

FIG. 3 is a side elevational view of a portion of the apparatus of FIG. l taken about lines 3 3 of FIG. 2.

FIG. 4 is a partially schematic, sectional view of the sodium generator forming a part of the amalgamator of the present invention.

FIG. 5 is a perspective view of the elements forming the mercury-sodium amalgam reactivation and circulating flow circuit of the present invention.

Turning to the drawings, the amalgamator 10 of the present invention comprises a number of principle elements including: a fixed recovery cell 12 incorporating a stationary acrylic plastic trough 14 and an endless conveyor 16 forming the individual movable cells, fixed ore supply and delivery means 18, tailing discharge means 20, and a mercury-sodium amalgam circulating and activating system incorporating the mercury amalgam reservoir 22, Wash tank 24, pump 26, filter 28 and sodium generator 30.

In essence, the recovery cell 12 is one big well or trap, but it is used in a rather unique manner. The endless conveyor 16 comprises a pair of endless chains 32 which support transversely extending carbon anodes 34 which have xed thereto, rubber paddles or Scrapers 36, the adjacent paddles defining therefore individual cells 38 by having the paddle ends or tips 40 disposed within the ore slurry 44 just above the mercury pool 42. Pool 42 forms a liquid mercury cathode and acts on the slurry in a known electrolytic manner by the passage of current between the moving carbon anodes 34 and the activated mercury-sodium amalgam 42. The action of the rubber paddles gently rolls the ore slurry 44 across the constantly activated shallow pool of mercury 42. Under the principles of the present invention, this pool could cover a tremendous area. Conceivably, an activated pool of mercury of 32 square feet is well within the limits of effective amalgamation. For instance, in the present apparatus, the pool may be four feet wide and eight feet long. The conveyor then comprises four compartments for each running foot with the conveyor traveling at a speed of one foot every two seconds. Thus, the apparatus would operate at roughly 1800 feet per hour. Employing the spaced rubber Scrapers or paddles 36, 7200 activated compartments move across the mercury pool each hour. This approach is in contrast to conventional systems which require a large volume of Water to move the amount of material between the cathode and anode in either a gravity or water powered device. The method of the present invention employs very little water (solution) which is constantly being recirculated, and none for the moving of materials, since the powered conveyor causes the ore in slurry form t0 move across the separated mercury beds.

All elements of the apparatus are supported by frame members in the form of I-beams or the like fixed to a base member 46. For instance, vertical beams 48, 50 and 52 are joined by horizontal beams 56 and 58 to provide an open support system for the amalgamator components.

The fixed trough 14 is provided with an enlarged ore bin and delivery section 18 which opens up horizontally into the trough as indicated in FIG. 3 and is provided with an inclined bottom surface 60 leading from a mechanical stoker 62. Thus, the platinum or gold ore deposited within ore bin 18 as indicated by arrow 64 and the mechanical stoker 162 constantly feeds fresh ore to the continuously moving endless conveyor 16. The rubber paddles or scrapers 40 pick up the ore from the stoker 462 and move it from left to right through the amalgamator I10, FIG. 1. At the discharge end of the trough '12, th conveyor 16 is so arranged that the rubber scrapers 36 serve as drag de-watering devices. Only damp ore will be discharged, the solution running back to the trough main floor section 68 and specifically, down the inclined discharge fioor 66. To eliminate any carry over of material by the conveyor, a fine spray of water from spray means 70 is directed onto the conveyor paddles 36 as they move along an upwardly inclined path. This spray water will run through the trough 12 and serve as make up solution. Preferably, the trough 12 is provided with overflow holes (not shown) in the vicinity of the ore bin 18. In ore containing a heavy slime fraction, the slimes may be settled out and the solution may be recirculated by auxiliary settling tanlks although for simplicity purposes, these means are not shorwn in the present amalgamator. Further, the rubber paddles are so designed as to allow for flow back of the soltuion, the paddles having their ends notched at 72 (FIG. 2). The large longitudinal I-beams 54 and 56, respectively, carry top and bottom endless conveyor shafts 74 and 76. The shafts are mounted for rotation about their axes by suitable bearings 78. Fixed to the shafts are the chain supporting and driving sprockets y80 wvith conveyor drive motor 82 being coupled to one of the sprockets 80 being coupled to the top drive shaft 74 through a gear reduction mechanism and speed control means 84. Thus, the endless conveyor is driven at an appropriate speed in a counter-clockwise direction as viewed in FIGS. 1 and 3. The fixed trough 14 is divided into a number of separate generally equal compartments by partition members or spacers 86 with the conveyor 16 extending beyond the compartments formed by the dividers 86 a distance, of roughly 1 foot or more. This dimension is important particularly at the discharge end since the liquid forming the ore slurry is recirculated and controlled in the manner previously referred to. Preferably, the mercury trough 14 is removable and adjustable; that is, it may be raised and lowered by 'jacking bolts (not shown). The bottom of trough 14 therefore forms a bed 42 of activated mercury generally 1A of an inch to 1/2 of an inch deep. Activated mercury is separately fed to and discharged from each of the compartments 128, 130, 132 and 134 formed by the mercury bed dividers 68. If it is assumed that the apparatus has four compartments roughly one footilwide and five feet long, mercury weighing 1/2 pound to the square inch, there Will be from 18 to 36 pounds of mercury for each of the four compartments and if the mercury is completely recycled every 30 minutes, fed, drained, filtered, and reactivated, the mercury pump 26 'will have to handle anywhere from 180 to 360 pounds of mercury per hour. The mercury pump 26 is conventional, being driven by pump motor 88 through mechanical coupling 90. A satisfactory pump is manufactured by the Myno Company for instance, and has a positive spline-type action. The mercury is collected from the individual compartments through mercury outlet pipes 92, the pipes being coupled by 'a common inclined conduit 94 to rwash tank 24, wherein the precious metal which has been picked up by the mercury sodium amalgam is removed in a conventional manner. The mercury is recirculated by the mercury pump 26 which is connected to the Wash tank by conduit 96. The discharge of the mercury passes by means of vertical conduit 98 to filter 28 which is carried by the upper transverse beam 58 of the amalgamator frame. The filter 2S is conventional, for example, a filter known on the market as a Micro-Clean filter, the filter delivers mercury through conduit 100 to the sodium` generator 30 for reactivation. The Micro-Clean filter employs a plastic cage which is easily removable and carries inside a cartridge made of stainless steel cloth with this also being easily removable. Two or more such filters may be employed allowing the mercury return circuit to be switched from one to the other with the ones not being presently used being removed from the circuit to enable cleaning of the filter.

The operation of the sodium generator may be seen best by reference to FIG. 4. The sodium generator consists of a rectangular container $102 'including a cover 104 which is provided lwith depending partition members 106 having their ends disposed within the mercury 108 which due to its specific gravity is maintained at the bottom of the generator, in contact with the carbon or iron cathode member 110. Multiple carbon or graphite anodes 112 are provided for the sodium generator, the cathode being immersed in and in contact with the mercury bath 108 which forms a mercury cathode with respect to the spaced carbon anodes 112. The sodium generator therefore comprises an electrolytic cell approximately square inches in the area of the anode and cathode and uses a voltage of from 3.75 to 4.25 volts and a current of approximately 1 amp per square inch, the unit producing pounds of mercury per hour of M0 of one percent sodium amalgam. The source of DC voltage (not shown) is coupled across anode terminal 113 and cathode terminal 115. The saturated solution of sodium chloride which is captured between the partitions 106 and indicated at 114 is constantly being circulated from a box of container i116 of thersame through a circuit including the brine pump 118 'and inlet and outlet conduits 120 and 112, respectively. Meanwhile, mercury requiring reactivation is being delivered from the filter 28 to inlet conduit 100 and discharged after treatment through the outlet conduit 124. From outlet conduit 124, the activated sodium mercury amalgam passes to the hydrogen reservoir 22, where the overflow passes by means of individual mercury feed pipes 126, to the trough 12 and specifically the four individual compartments 1218, 130, 132 and 134. The rate of -flow of mercury-sodium` amalgam may be individually adjusted by the valves 136 within each inlet line 12.6.

The schematic or flow diagram of FIG. =5 for the sodium-mercury amalgam is slightly different from the specific apparatus of FIG. 1, but only in the configuration of the elements forming the components thereof, principally the shape of the trough 14 and the coupling and position of the mercury pump and drive means relative to the wash tank 24.

The electrolyte in the form of saturated solution of sodium chloride is constantly recirculated by pump 118 from a brine tank 116 with the electrolyte tiowing counter current to the mercury `fiow as evidenced from FIG. 4. The source of direct current and the method of coupling to cathodes and anodes 112 of the sodium generator are not shown, but in this respect and also the general configuration of the sodium generator, are quite conventional. Likewise, direct current is delivered to the iron cathode 138 and the fixed bus bar 140 is delivered through electrical leads 142 from a source (not shown).

There may be conditions where a plating surface other than a mercury pool may be required. A perforated plate, 1A of an inch in thickness and 1 foot square of copper or other material may be placed in one or all four of the compartments 128 through 134. A single plate 150 having perforations is shown in compartment 130. The plate is not attached to the trough 14 in any way, but merely floats on the bed 42 of mercury. The plate 150 is held in place by the rubber paddles 36 as they move across the plate surface. The only pressure comes from the buoyancy of the mercury acting on the plate. The perforations 152 serve as mercury under current. Preferably, the edges of the plate are bent downward; that is, they are given a slight break at each end to avoid hanging up on the paddles. The plate being formed of copper does not act adversely to the action set up between the moving blocks anodes 34 and the mercury cathode.

In operation the system is continuously driven; that is, both the mercury pump motor 88 and the conveyor chain drive motor 82 are continuously energized to cause circulation of the mercury through the activating and the precious metal recovery components while conveyor 16 forces the ore slurry through the amalgamator. The conveyor speed provided by the gear reduction means 80 is on the order of feet per minute or higher, depending upon the ore characteristics. Electrical current is also constantly being supplied to the spaced anode 112 and cathodes 110 in the sodium generator, as well as between the individual mercury cathodes formed by the mercury pool 42 and the moving carbon anodes 34 of the conveyor 16. Thus, the mercury is being impregnated with metallic sodium to form the amalgam within the sodium generator. The circulating constantly reactivated mercury amalgam with sodium as the collector facilitates the removal, under electrolytic action, of the precious metal from the ore slurry and carries the same to the wash tank 24 for separation therefrom. When a particle of gold, for example, is brought into contact with the mercury by concentration from the pulp, the galvanic action at the point of contact of the mercury with the gold is intensified due to the presence of the sodium. The electrolytic action, however, robs the mercury of the sodium and reduces the required amalgamation action. Therefore the mercury after removal of the precious metal requires reactivation at the sodium generator 30.

From the above, it is seen that the controlled electrolysis is beneficial to the system since, it reduces the ilm coating on the gold by the hydrogen created during electrolysis with the gold being then readily wetted by the mercury-sodium amalgam to cause the precious metal to sink into the mercury for subsequent removal. Movement of the released hydrogen tends to stir and disturb the ore particles tending to classify them and move the heavier fraction downward to contact the amalgam for removal. It is also helpful in freeing absorbed and chemically combined values. Since the invention to a -great extent involves the movement of the ore across a bed of continuously activated mercury in a positive manner, while a constant electrical potential is applied, the system provides great flexibility in the control of the rate of ore slurry being fed, the rate of electrolyte feed and its composition, the required dilution of the ore slurry being fed, the optimum retention time of the ore slurry in contact with the mercury bed, and the factors involving electrolysis in the trough.

It is additionally seen that the recovery of precious metals by amalgamation with mercury is a relatively simple and highly eiiicient process, provided that both the mercury and the precious metal are clean. Lode or placer gold or silver that is filmed by oxides, sulfdes, tellurides or foreign coatings of any nature cannot be amalygamated. Even clean gold or silver cannot be amalgamated by mercury which is not clean. In the amalgamator of the present invention, means are provided whereby the cleanliness and reactivity of the mercury is assured principally through its continuous recirculation through lters and a cell in which sodium is added to form the sodium amalgam. Electrolysis of the pulp with the amalgam as the cathode accelerates wetting of the precious metal completing the reduction of the interference lm which may not be reduced completely by oxidizing activity at the anode.

In the conventional amalgamation, water is added to the ore. The present invention involves an apparatus in which it is found advantageous to add reagents to the Water to act as electrolytes. For example, alkaline dyanide or sodium chloride may be employed. These reagents are particularly valuable when the apparatus or the present invention carries ore in the form of finely divided values not recoverable by conventional amalgamating methods. These finely divided values, when treated under electrolysis, the solution of the values is accelerated at the anode while decomposition at the cathode puts them into the cathode (sodium amalgam). The mercury sodium amalgam will also pick up other metals, the majority of these being removed by ltration. The amalgam which is essentially low in these elements is then returned to the circuit.

Electrolytic decomposition of the saturated sodium chloride solution to form the sodium amalgam constantly depletes the solution. Depletion is balanced by the constant addition of sodium chloride, The electrolyte or transport solution, since it is being maintained by the configuration of the trough, may foul during use. Any difliculty which may arise from fouling of the recirculated solution is obviated by bleed-off and replacement. The optimum density of the pulp being treated varies from 2/1 to 10/ 1, depending upon the nature of the ore. At the same time, the optimum electrical potential which is applied depends upon the conductivity of the electrolyte used in the nature of the ore being treated. It may vary from a low of 1'1/2 volts to an undetermined upper limit.

The apparatus of the present invention is operated in conformance with the following examples:

EXAMPLE 1 A pulp is made up of 1 part of ground ore by weight to l0 parts of a 0.3% solution of sodium cyanide in Water saturated with calcium hydroxide. The pulp electrolyzed for two minutes at 2 volts with a graphite anode and a sodium amalgam cathode.

Sample 'assay by 48 hour conventional cyanide: 0:3 oz.

gold Result of amalgamation, Example l: 0.32 oz. gold EXAMPLE 2 A pulp is made up of one part of ground ore by weight to l0 parts of a 0.1% solution of sodium chloride in water. The pulp electrolyzed for two minutes at two volts with a graphite anode and a sodium amalgam cathode.

Sample assay by 48 hour conventional cyanide: `0.3 oz.

gold Result of Example 2: 0.31 oz. gold While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that the foregoing and other changes in the form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. An amalgamator comprising:

a generally fixed, horizontal trough having outwardly inclined ends,

spaced transverse dividers carried by said trough along the bottom thereof for separating a layer of mercury carried by said trough into separate but adjacent portions,

an endless conveyor mounted above said trough and extending longitudinally at both ends beyond the trough bottom so as to overlie said inclined ends,

a plurality of paddles carried by said endless conveyor and extending radially outward therefrom with the tips of said paddles moving over said mercury,

an opening within one end of said trough through said inclined end above the bottom thereof for introducing metal ore bearing slurry into said trough for movement over said mercury layer by means of said endless conveyor such that the tips of said paddles move over said mercury but are emersed in said slurry to move the same from said inlet end of said trough to said inclined outlet end,

spaced anodes carried by said endless conveyor on respective paddles and forming rst electrode means,

a stationary, energized bus bar in juxtaposition to said moving anodes and in contact therewith, the edges of said paddles being recessed to allow electrolyte to ow counter to their motion and to facilitate even distribution of'electrolyte within said trough and above said mercury layer, and

means for continuously circulating said mercury layer through said trough by separate feed paths to each mercury layer portion including selectively controlled valve means to regulate the flow of mercury to said separate portions.

2. The amalgamator as claimed in claim 1, further comprising:

common mercury collecting means fluid coupled to said individual trough portions,

means including said common collecting means for washing said mercury to remove the precious metal picked up by the mercury-sodium amalgam,

an electrolytic cell sodium generator for re-activation of the mercury amalgam after removing the precious metal,

a pump for pumping the mercury amalgam from the wash tank to the sodium generator,

lter means intermediate of said pump and said generator for ltering the mercury prior to re-activation, and

means for delivering re-activated sodium-mercury amalgam from said regenerator to said individual trough JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant `Examiner U.S. Cl. X.R. 

